Danilo Skoczowsky

Tuning high-power laser diodes with as much as 0.38 W of power and M 2 = 1.2 over a range of 32 nm with 3-GHz bandwidth

Gain-guided diode lasers usually have emission wavelengths determined by the manufacturing process, with typically 0.5-1-nm bandwidth. Furthermore, their beam quality is rather poor. We show that external cavities allow for tunable narrow-bandwidth operation of gain-guided diode lasers. At the same time the beam quality is drastically improved; almost diffraction-limited light of more than 200 mW has been achieved over the whole tuning range from 910 to 942 nm with narrow bandwidth.

Stripe-array diode-laser in an off-axis external cavity: theory and experiment.

Stripe-array diode lasers naturally operate in an anti-phase supermode. This produces a sharp double lobe far field at angles +/-alpha depending on the period of the array. In this paper a 40 emitter gain guided stripe-array laterally coupled by off-axis filtered feedback is investigated experimentally and numerically. We predict theoretically and confirm experimentally that at doubled feedback angle 2alpha a stable higher order supermode exists with twice the number of emitters per array period. The theoretical model is based on time domain traveling wave equations for optical fields coupled to the carrier density equation taking into account diffusion of carriers. Feedback from the external reflector is modeled using Fresnel integration.

Efficient second-harmonic generation using a semiconductor tapered amplifier in a coupled ring-resonator geometry

A new approach for efficient second-harmonic generation using diode lasers is presented. The experimental setup is based on a tapered amplifier operated in a ring resonator that is coupled to a miniaturized enhancement ring resonator containing a periodically poled lithium niobate crystal. Frequency locking of the diode laser emission to the resonance frequency of the enhancement cavity is realized purely optically, resulting in stable, single-frequency operation. Blue light at 488 nm with an output power of 310 mW is generated with an optical-to-optical conversion efficiency of 18%.

100 mW high efficient single pass SHG at 488 nm of a single broad area laser diode with external cavity using a PPLN waveguide crystal

A frequency stabilized single broad area laser in a V-shaped external cavity is used for Second Harmonic Generation (SHG) in a waveguide channel with dimensions of 3 mum x 5 mum x 10 mm of a PPMgO: LN crystal. A maximum coupling efficiency of 63% could be obtained. An optical output power of 100.4 mW of visible light at 488 nm could be generated with 265 mW of coupled infrared light. This results in a single pass conversion efficiency of 37.8%. No photorefractive damage or saturation effects were observed.

Multi-wavelength, high spatial brightness operation of a phase-locked stripe-array diode laser

Stable continuous wave multi-wavelength operation of a stripe-array diode laser with an externalcavity spectral beam combining geometry is presented. In this setup each emitter of the stripe-array is forced to operate at a different wavelength, which leads to a decoupling between the usually phase-locked emitters. With a reflective diffraction grating with a period of 300 lines per mm, 33 equidistant laser lines around a center wavelength of 978 nm were realized, spanning a spectral range of 26 nm. With this novel approach near-diffraction limited emission with a beam quality of M2 < 1.2 and an output power of 450 mW was achieved. This laser light source can be used for applications requiring low temporal but high spatial coherence.

Highly efficient single pass blue light generation at 488 nm using a PPKTP waveguide crystal and high brightness diode lasers

The combination of high brightness laser diodes and periodically poled (PP) waveguide crystals for the generation of blue light at the technically interesting wavelength of 488 nm is promising. Although PPKTP has a lower nonlinear coefficient compared to PPLN it is of interest for the use in such devices. Because of its higher photorefractive damage threshold, it is well suited for operation at room temperature. In this work, a DFB laser as well as a tunable external cavity enhanced broad area diode laser (ECDL) are used for second harmonic generation using a waveguide PPKTP crystal. Both lasers yield several hundred Miliwatts of diffraction limited light around a center wavelength of 976 nm with excellent spectral properties. The ECDL system is further tunable over a broad range of 40 nm. The PPKTP crystal has a length of 12 mm and the 4 μm x 8 μm waveguides are manufactured by ion exchange followed by a patented submount poling technique. By using a DFB laser diode as pump source a laser to waveguide coupling efficiency of more than 55% could be achieved. A maximum output power of 66.7 mW could be generated out of 220 mW infrared light inside the waveguide channel at room temperature. This results in a conversion efficiency of more than 260%/W.

High-brightness emission from stripe-array broad area diode lasers operated in off-axis external cavities

Phase-coupled stripe-array diode lasers show a strong double-lobed far-field because adjacent stripes tend to operate in the anti-phase supermode. One way to achieve a stable phase relationship and global coupling of the emitters of such a stripe-array is off-axis feedback. In this work several off-axis external cavity designs are discussed. A 400 μm wide emitter stripe array consisting of 40 stripes with a pitch of 10 μm was investigated. By operating this device in a Littrow type off-axis external cavity, more than 2 W of output power of near diffraction-limited, single longitudinal mode emission with a brightness as high as 88 MW/cm2-str could be achieved. The technique of off-axis feedback was also adapted to realize spectral beam combining of 25 emitters of a laser bar. The experimental data are compared with numerical simulations using a new theoretical model including feedback.

Direct Generation of 50 ps-Pulses from an External Cavity Diode Laser Yielding 200 mW Average Output Power

We present a broad area diode laser with a very simple external resonator which shows self-induced modelocking of about 10 longitudinal modes at a repetition rate of 1-3 GHz, resulting in short pulses.

ps-Pulse generation by self-induced modelocking of a high power broad area diode laser in an external resonator

Up to 250 mW of ps-pulses with a pulsewidth of 50 ps and a repetition rate of 1-3 GHz are generated by self-induced modelocking of a high-power diode-laser working in an external resonator.

Coupled ring resonator geometry for efficient second harmonic generation

Generation of visible light by second-harmonic generation (SHG) of diode laser radiation using enhancement cavities with a nonlinear crystal is a well established technique. The main problem is to lock the laser emission to the resonance frequency of the enhancement cavity or vice versa. The two common approaches are electronic or optical locking. In electronic locking, an error signal proportional to the frequency detuning is generated [1]. This signal can be applied, e. g., to the driving current of the diode laser or to a piezo-controlled mirror. In optical locking, light is injected into the laser to force the laser emission to the resonance frequency of the enhancement cavity. Therefore, the enhancement cavity itself can be used to filter out the appropriate frequency [2].